Method of forming an intermetal dielectric layer

ABSTRACT

A method is used to form an intermetal dielectric layer. According to the invention, an unbiased-unclamped fluorinated silicate glass layer used as a protection layer is formed by high density plasma chemical vapor deposition on a biased-clamped fluorinated silicate glass layer formed by high density plasma chemical vapor deposition to prevent the biased-clamped fluorinated silicate glass layer from being exposed in a planarization process.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a method for forming an integratedcircuit, and more particularly, to a method for forming an intermetaldielectric layer with multilevel interconnects.

[0003] 2. Description of the Related Art

[0004] In an integrated circuit with two or more levels ofinterconnects, an intermetal dielectric layer must be placed between thelevels for isolation. Generally, the intermetal dielectric layer musthave characteristics such as good reliability, good mechanicalstability, good compatibility, low water absorption capability, etc.

[0005] A typical material for the intermetal dielectric layer is siliconoxide that has a dielectric constant of about 4. However, since a devicehaving a higher operation speed requires a material having a lowerdielectric constant as the intermetal dielectric layer, fluorinatedsilicon glass (FSG) having a dielectric constant of about 3.5 isreplacing the silicon oxide as the intermetal dielectric layer.

[0006] According to the prior art, the method to form the intermetaldielectric layer is as follows. A plurality of metal conductive lines isformed on a substrate. The plurality of metal conductive lines isdistributed in two regions, respectively, a tied conductive line region(i.e. a dense line region) having a higher distribution density and aloose conductive line region (i.e. a iso line region) having a lowerdistribution density. A biased-clamped FSG layer is formed on thesubstrate by high density plasma chemical vapor deposition (HDPCVD), andfills gaps between metal lines. Before the biased-clamped FSG layer isformed, the process further comprises forming a silicon glass linerlayer by HDPCVD. The silicon glass liner layer is used to prevent themetal lines from being attacked by fluorine. Then, an oxide layer isformed as a cap layer on the biased-clamped FSG layer by plasma enhancedchemical vapor deposition (PECVD). A chemical mechanical polishingprocess is subsequently performed on the oxide layer.

[0007] Due to different distribution densities, the spacing betweenconductive lines in different regions (the tied conductive line regionand the loose conductive line region) is different. This may result in alarge step height difference between the tied conductive line region andthe loose conductive line region after the biased-clamped FSG layer andthe cap layer are formed. Thus, the polishing stop for chemicalmechanical polishing is difficult to control, and over-polishing easilyarises. As a result, the biased-clamped FSG layer may be exposed. Sincethe amount of fluorine in the biased-clamped FSG layer is difficult tocontrol, and the biased-clamped FSG layer exhibits intrinsicallyhydrophilic behavior, the biased-clamped FSG layer easily absorbs waterwhen the biased-clamped FSG layer contacts is in contact with an aqueousbase slurry during chemical mechanical polishing process. Thus, thereaction product produced during chemical mechanical polishing processcan result in metal corrosion, oxide degradation. peeling at themetal/intermetal dielectric layer interface, and an increased dielectricconstant. Furthermore, when a metal plug is formed, the HF can poisonthe metal plug. the contact resistance is increased and the increasedcontact resistance can affect the subsequent process.

SUMMARY OF THE INVENTION

[0008] According to above, the invention provides a method for formingan improved intermetal dielectric layer. In order to prevent thebiased-clamped FSG layer from being exposed, the method provides anunbiased-unclamped FSG layer as a protect layer on the biased-clampedFSG layer.

[0009] The method comprises the following steps. A plurality of metallines is formed on a substrate. A biased-clamped FSG layer is formed onthe substrate by HDPCVD. An unbiased-unclamped FSG layer as a protectionlayer is formed on the biased-clamped FSG layer by HDPCVD. An oxidelayer as a cap layer is formed on the protection layer. A planarizationprocess is performed on the oxide layer.

[0010] The unbiased-unclamped FSG layer is used as a protection layer inthe invention to prevent the biased-clamped FSG layer from being exposedduring a planarization process and attacked by water.

[0011] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary, andare intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1A through FIG. 1C are schematic, cross-sectional viewsshowing a process for forming an intermetal dielectric layer accordingto a first preferred embodiment of the invention;

[0013]FIG. 2 shows the relationship between the penetration depth (nm)in the unbiased-clamped FSG layer and hydrogen concentration usingSecondary Ion Mass Spectroscopy (SIMS); and

[0014]FIG. 3 shows the relationship between the penetration depth (nm)in the unbiased-clamped FSG layer and fluorine concentration usingSecondary Ion Mass Spectroscopy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] FIGS. 1A through FIG. 1C are schematic, cross-sectional viewsshowing a process for forming an intermetal dielectric layer accordingto a first preferred embodiment of the invention.

[0016] Referring to FIG. 1A, a substrate 100 is provided. A plurality ofmetal conductive lines 102 a, 102 b, and 102 c is formed on thesubstrate 100. A tied conductive line region 104 a and a looseconductive line region 104 b consist of the plurality of metalconductive lines 102 a, 102 b, and 102 c.

[0017] Referring to FIG. 1B, a dielectric layer 106 is formed on thesubstrate 100. Due to different spacings among the metal conductivelines 102 a, 102 b, and 102 c, the height of the dielectric layer 106 isnot uniform. The dielectric layer 106 comprises biased-clampedfluorinated silicon glass (FSG) formed by, for example, high densityplasma chemical vapor deposition (HDPCVD). The dielectric constant ofthe biased-clamped FSG is about 3.5, which depends on the processvariation. The FSG is widely used as an intermetal dielectric materialbecause of its low dielectric constant, capability of decreasingcapacitance between interconnects, and good gap-filling capability.

[0018] In addition, before forming the dielectric layer 106, an undopedsilicon glass liner layer can be formed on the substrate 100 by, forexample, HDPCVD. Since the undoped silicate glass liner layer has goodcompatibility with the FSG layer, the undoped silicate glass liner layercan promote adhesion between the FSG layer and another material layerand benefit the subsequent process.

[0019] Although the dielectric constant of the undoped silicon glassliner layer is about 4.1, it is very thin; thus, the undoped siliconglass liner layer does not affect the overall dielectric constant of theinternetal dielectric layer.

[0020] A protection layer 108 is formed on the dielectric layer 106. Theprotection layer 108 comprises unbiased-unclamped FSG formed by, forexample, HDPCVD. The dielectric constant of the unbiased-unclamped FSGis about 3.5, which thickness depends on the process. “Unbiased” meansthat no bias is applied during performing the HDPCVD, and “unclamped”means that there is no helium cooling device on the backside of thesubstrate 100 during the deposition, or that no helium cooling processis performed on the substrate 100 during the deposition.

[0021] Since the depositing rate of the unbiased-unclamped FSG layer(the protection layer 108) formed by HDPCVD is greater than that of thebiased-clamped FSG layer (the dielectric layer 106) formed by HDPCVD,the throughout is not affected by the process of first forming thedielectric layer 106 to a thinner thickness than in the prior art andthen forming the protection layer 108 to an adequate thickness.

[0022] Since the dielectric constant of the protection layer 108 isnearly the same as that of the dielectric layer 106, the protectionlayer 108 does not affect the overall dielectric constant of theintermetal dielectric layer.

[0023] A cap layer 110 is formed on the protection layer 108. The caplayer 110 is, for example, an oxide layer formed by HDPCVD or by PECVD.Referring to FIG. 1C, a planarization process such as chemicalmechanical polishing (CMP) is performed on the cap layer 110.

[0024] Since the unbiased-unclamped FSG layer has a lower waterabsorption capability than the conventional FSG layer, if theunbiased-unclamped FSG layer is exposed due to the chemical mechanicalpolishing process, the unbiased-unclamped FSG layer does not react withan aqueous slurry or water to produce hydrogen fluoride (HF). Thus, theprotection layer 108 can prevent the dielectric layer 106 from beingover-etched as occurred in the prior art.

[0025]FIG. 2 shows the relationship between the penetration depth (nm)in the unbiased-unclamped FSG layer and hydrogen concentration usingSecondary Ion Mass Spectroscopy (SIMS). FIG. 3 shows the relationshipbetween the penetration depth (nm) in the unbiased-clamped FSG layer andfluorine concentration using secondary ion mass spectroscopy.

[0026] Referring to FIG. 2 and Table 1, there is no obvious change inthe hydrogen concentrations before and after CMP. This indicates thatthe unbiased-unclamped FSG layer efficiently prevents the HF from beingproduced, and further prevents metal corrosion, oxide degradation,peeling at the metal/intermetal dielectric layer interface, and anincreased dielectric constant. TABLE 1 Fluorine concentration inHydrogen concentration in percentage (%)* percentage (%)** Before the13.17 0.140 CMP After the CMP 13.13 0.126

[0027] Referring to FIG. 3 and Table 1, there is no obvious variation inthe fluorine concentrations before and after CMP. This indicates thatthe unbiased-unclamped FSG layer efficiently prevents the HF from beingproduced, and further prevents metal corrosion, oxide degradation,peeling at the metal/intermetal dielectric layer interface. and anincreased dielectric constant.

[0028] In addition, the invention not only applies to the multilevelinterconnect process, but also applies to, for example, the metal plugprocess, the dual damascene process, the dielectric layer depositingprocess between the conductive lines, etc.

[0029] Other embodiments of the invention will appear to those skilledin the art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method for forming an intermetal dielectriclayer, comprising: providing a substrate; forming a plurality of metalconductive lines on the substrate, wherein a tied conductive line regionand a loose conductive line region consist of the plurality of metalconductive lines, forming an intermetal dielectric layer on thesubstrate; forming a protection layer on the intermetal dielectric layerwherein the protection layer is thinner than the intermetal dielectriclayer; forming a cap layer on the protection layer; and performing aplanarization process.
 2. The method for forming the intermetaldielectric layer according to claim 1 wherein the intermetal dielectriclayer comprises fluorinated silicon glass.
 3. The method for forming theintermetal dielectric layer according to claim 1 . wherein the formationof the intermetal dielectric layer comprises biased-clamped high densityplasma chemical vapor deposition.
 4. The method for forming theintermetal dielectric layer according to claim 3 . wherein thebiased-clamped high density plasma chemical vapor deposition isperformed under a bias and helium cooling is employed.
 5. The method forforming the intermetal dielectric layer according to claim 1 , whereinthe protection layer comprises fluorinated silicon glass.
 6. The methodfor forming the intermetal dielectric layer according to claim 1 ,wherein the formation of the protection dielectric layer comprisesunbiased-unclamped high density plasma chemical vapor deposition.
 7. Themethod for forming the intermetal dielectric layer according to claim 6, wherein the unbiased-unclamped high density plasma chemical vapordeposition is performed without a bias and without helium cooling. 8.The method for forming the intermetal dielectric layer according toclaim 1 , wherein the protection layer is used as a stop layer.
 9. Themethod for forming the intermetal dielectric layer according to claim 1, wherein the cap layer comprises an oxide layer.
 10. The method forforming the intermetal dielectric layer according to claim 1 , whereinthe formation of the cap layer comprises plasma enhanced chemical vapordeposition.
 11. The method for forming the intermetal dielectric layeraccording to claim 1 , wherein before forming the intermetal dielectriclayer, the process further comprises forming a undoped silicon glasslayer.
 12. The method for forming the intermetal dielectric layeraccording to claim l wherein the planarization process comprises achemical mechanical polishing process.
 13. A method for forming anintermetal dielectric layer, comprising: providing a substrate; forminga plurality of metal conductive lines on the substrate; forming a firstdielectric layer on the substrate; forming a second dielectric layer onthe first dielectric layer; forming a cap layer on the second dielectriclayer; and performing a planarization process.
 14. The method forforming the intermetal dielectric layer according to claim 13 , whereinthe formation of the intermetal dielectric layer comprisesbiased-clamped high density plasma chemical vapor deposition.
 15. Themethod for forming the intermetal dielectric layer according to claim 14, wherein the biased-clamped high density plasma chemical vapordeposition is performed under a bias and helium cooling is employed. 16.The method for forming the intermetal dielectric layer according toclaim 13 wherein the formation of the protection dielectric layercomprises unbiased-unclamped high density plasma chemical vapordeposition.
 17. The method for forming the intermetal dielectric layeraccording to claim 16 , wherein the unbiased-unclamped high densityplasma chemical vapor deposition is performed without a bias and withouthelium cooling.
 18. The method for forming the intermetal dielectriclayer according to claim 13 , wherein the cap layer comprises an oxidelayer.
 19. The method for forming the intermetal dielectric layeraccording to claim 13 wherein the second dielectric layer is used as astop layer.
 20. The method for forming the intermetal dielectric layeraccording to claim 13 , wherein before forming the first dielectriclayer, the process further comprises forming an undoped silicon glasslayer.
 21. A method for forming an intermetal dielectric layer, whereinthe method applies to a substrate and a plurality of metal conductivelines is formed on the substrate, the method comprising: forming adielectric layer on the substrate; forming a protection layer on thedielectric layer; forming a cap layer on the protection layer; andperforming a planarization process.
 22. The method for forming theintermetal dielectric layer according to claim 21 , wherein theformation of the intermetal dielectric layer comprises biased-clampedhigh density plasma chemical vapor deposition.
 23. The method forforming the intermetal dielectric layer according to claim 22 , whereinthe biased-clamped high density plasma chemical vapor deposition isperformed under a bias and helium cooling is employed.
 24. The methodfor forming the intermetal dielectric layer according to claim 21 ,wherein the protection layer comprises fluorinated silicon glass. 25.The method for forming the intermetal dielectric layer according toclaim 21 , wherein the formation of the protection dielectric layercomprises unbiased-unclamped high density plasma chemical vapordeposition.
 26. The method for forming the intermetal dielectric layeraccording to claim 25 , wherein the unbiased-unclamped high densityplasma chemical vapor deposition is performed without a bias and withouthelium cooling.
 27. The method for forming the intermetal dielectriclayer according to claim 21 , wherein the cap layer comprises an oxidelayer.
 28. The method for forming the intermetal dielectric layeraccording to claim 21 , wherein the second dielectric layer is used as astop layer.